Pneumonia — Community & Hospital Acquired

Pneumonia is an acute infection of the lung parenchyma (alveoli and distal airways) producing consolidation. For NEET PG, the highest-yield areas are causative-organism matching, CURB-65 risk stratification, atypical pneumonia clues, HAP/VAP definitions, empirical antibiotic choice, aspiration sites, and complications like parapneumonic effusion, empyema and lung abscess.

Definition & Classification

Pneumonia = inflammation of the lung parenchyma, usually infective, with new radiographic infiltrate plus clinical signs (fever, cough, purulent sputum, dyspnoea, pleuritic chest pain, signs of consolidation).

Classification is best remembered by epidemiological setting, because this drives the likely organism and empirical therapy:

Type	Definition	Common organisms
CAP (Community-Acquired)	Onset in community or <48 h of admission	S. pneumoniae (commonest overall), Mycoplasma, H. influenzae, Legionella, viruses
HAP (Hospital-Acquired)	Onset ≥48 h after admission, not incubating at admission	Pseudomonas, S. aureus (incl. MRSA), Klebsiella, Acinetobacter, Enterobacter
VAP (Ventilator-Associated)	Onset ≥48 h after endotracheal intubation	Pseudomonas, MRSA, Acinetobacter, GNBs
HCAP	(Older term, now largely abandoned)	—
Aspiration	Inhalation of oropharyngeal/gastric contents	Anaerobes, mixed flora

High-yield: Streptococcus pneumoniae (pneumococcus) is the single most common cause of CAP across all age groups and severities. It is the classic cause of lobar pneumonia.

Anatomically: lobar (whole lobe, classically pneumococcus), bronchopneumonia (patchy, around bronchi, often Staph/Klebsiella), and interstitial/atypical (diffuse, Mycoplasma, viruses, Pneumocystis).

Etiology & Pathophysiology

Organisms reach the lung mainly by micro-aspiration of oropharyngeal secretions; less often by inhalation of aerosols (Legionella, TB, viruses), haematogenous spread (right-sided endocarditis → S. aureus), or contiguous spread.

The four classic pathological stages of lobar pneumococcal pneumonia:

1. Congestion (day 1–2): vascular engorgement, serous exudate, bacteria. →
2. Red hepatisation (day 3–4): RBCs, neutrophils, fibrin fill alveoli; lung is firm, red, "liver-like". →
3. Grey hepatisation (day 5–7): RBCs lyse, fibrinosuppurative exudate, grey-brown firm lung. →
4. Resolution (>day 8): enzymatic digestion, macrophage clearance, restoration of architecture.

Organism-specific associations are heavily tested:

Organism	Classic clue / setting
S. pneumoniae	Rusty sputum, lobar consolidation, herpes labialis, splenectomy/sickle cell
Klebsiella pneumoniae	Alcoholics, diabetics; "red-currant jelly" sputum; bulging fissure sign; upper-lobe; abscess
Staph. aureus	Post-influenza, IV drug use; pneumatoceles, abscess, empyema, cavitation
Mycoplasma pneumoniae	Young adults, "walking pneumonia"; cold agglutinins; bullous myringitis; erythema multiforme
Legionella pneumophila	Air-conditioning/water systems; hyponatraemia, deranged LFTs, diarrhoea, relative bradycardia, confusion
Chlamydophila psittaci	Bird/parrot exposure (psittacosis); splenomegaly, Horder's spots
Coxiella burnetii	Q fever — cattle/sheep, parturient animals
Pseudomonas	CF, bronchiectasis, ventilated/ICU patients, neutropenia
Pneumocystis jirovecii	HIV with CD4 <200; dry cough, hypoxia out of proportion, bilateral perihilar infiltrates
Anaerobes	Aspiration, poor dentition, foul-smelling sputum, abscess

High-yield: Legionella → think the triad of pneumonia + hyponatraemia + relative bradycardia (Faget sign) + GI symptoms + confusion + raised transaminases. Diagnosed by urinary antigen (serogroup 1).

Atypical vs Typical Pneumonia

"Atypical" refers to organisms not seen on Gram stain / not cultured on standard media and not responsive to beta-lactams (they lack a cell wall or are intracellular).

Feature	Typical	Atypical
Organisms	Pneumococcus, H. influenzae, Klebsiella	Mycoplasma, Chlamydophila, Legionella, viruses
Onset	Acute, toxic	Subacute, insidious
Cough/sputum	Productive, purulent	Dry, scanty
CXR	Lobar consolidation	Patchy/interstitial, often worse than exam findings
Extrapulmonary	Few	Common (haemolysis, skin, GI, neuro)
Antibiotic	Beta-lactams work	Need macrolide / doxycycline / fluoroquinolone

High-yield: Mycoplasma pneumoniae produces cold agglutinins (IgM anti-I antibodies) causing autoimmune haemolytic anaemia; associated with erythema multiforme / Stevens-Johnson, bullous myringitis, Guillain-Barré, and a CXR that looks far worse than the patient.

Mnemonic for atypicals: "Legionnaires, Mycos, Chlamys, and Q-tips are atypical" (Legionella, Mycoplasma, Chlamydophila, Coxiella/Q fever).

Clinical Features

• Symptoms: fever with chills/rigors, productive cough, pleuritic chest pain, dyspnoea, malaise; elderly may present only with confusion, falls, or decompensation of comorbidity.
• Signs of consolidation: reduced chest movement, dull percussion note, increased vocal/tactile fremitus and vocal resonance, bronchial breath sounds, late inspiratory crackles, whispering pectoriloquy, aegophony (E-to-A change).

High-yield distinction (exam favourite): In consolidation, vocal resonance and fremitus are increased with bronchial breathing; in pleural effusion they are decreased with a stony-dull note and absent breath sounds.

CURB-65 — Severity Scoring

CURB-65 stratifies CAP severity and guides site of care. Score 1 point each:

Letter	Criterion	Cut-off
C	Confusion (new; AMTS ≤8)	—
U	Urea	>7 mmol/L (>19–20 mg/dL BUN)
R	Respiratory rate	≥30/min
B	Blood pressure	SBP <90 or DBP ≤60 mmHg
65	Age	≥65 years

Interpretation flow: Score 0–1 → outpatient (low mortality ~1.5%) → Score 2 → consider short hospital admission (~9%) → Score 3–5 → hospitalise, assess ICU (~22% mortality, often needs IV therapy).

High-yield: CRB-65 (drops urea) is used in primary care/where labs are unavailable: CRB-65 ≥1 warrants hospital assessment. Note the U cut-off = urea 7 mmol/L — a very common single-answer MCQ.

Other ICU-admission tools: IDSA/ATS minor criteria (need ≥3) and major criteria (septic shock needing vasopressors OR respiratory failure needing mechanical ventilation → automatic ICU). PSI/PORT score is more validated but cumbersome.

Diagnosis & Investigation of Choice

Investigation of choice for diagnosis: Chest X-ray (PA view) showing a new infiltrate is required to confirm pneumonia. CT chest is more sensitive when CXR is equivocal.

Supportive workup:

• CBC (neutrophilic leucocytosis; leukopenia = poor prognosis), CRP/procalcitonin (procalcitonin helps distinguish bacterial and guide antibiotic stopping).
• Sputum Gram stain & culture, blood cultures (before antibiotics in severe CAP/HAP).
• Urinary antigens: Legionella (serogroup 1) and S. pneumoniae.
• PCR / serology: Mycoplasma, Chlamydophila, respiratory virus panel, SARS-CoV-2.
• ABG / SpO₂, U&E (urea for CURB-65, Na for Legionella), LFTs.
• Pleural fluid analysis if effusion present — to exclude empyema/complicated effusion.
• HIV testing if Pneumocystis or recurrent pneumonia.

High-yield: Urinary Legionella antigen remains positive even after antibiotics are started — its big practical advantage over culture. Best specimen for Legionella culture is on BCYE (buffered charcoal yeast extract) agar with cysteine.

Management & Drug of Choice

Empirical therapy is by setting and severity. (Indian/British guideline-flavoured.)

CAP — outpatient (low severity, CURB-65 0–1): Amoxicillin is first-line. → If atypical suspected or penicillin allergy → macrolide (azithromycin/clarithromycin) or doxycycline.

CAP — hospitalised (moderate, CURB-65 2): Amoxicillin + macrolide (beta-lactam + atypical cover). Doxycycline is an alternative.

CAP — severe (CURB-65 3–5 / ICU): IV co-amoxiclav (or ceftriaxone) + IV macrolide, OR a respiratory fluoroquinolone (levofloxacin/moxifloxacin) as monotherapy alternative. Add anti-pseudomonal/MRSA cover if risk factors.

Organism-directed drug of choice:

Organism	Drug of choice
S. pneumoniae (sensitive)	Penicillin/amoxicillin
Mycoplasma / Chlamydophila	Macrolide or doxycycline
Legionella	Respiratory fluoroquinolone (levofloxacin) or azithromycin
MRSA pneumonia	Vancomycin or linezolid
Pseudomonas	Anti-pseudomonal beta-lactam (piperacillin-tazobactam/ceftazidime/meropenem) ± aminoglycoside
Pneumocystis jirovecii	Co-trimoxazole (TMP-SMX) + steroids if PaO₂ <70
Aspiration/anaerobes	Co-amoxiclav or clindamycin/metronidazole-containing regimen

HAP/VAP: cover Pseudomonas and resistant GNBs; add MRSA cover (vancomycin/linezolid) if risk factors (prior IV antibiotics in 90 days, high local MRSA prevalence). De-escalate based on cultures.

Supportive: oxygen (target SpO₂ 94–98%, or 88–92% if CO₂-retention risk), fluids, antipyretics (paracetamol), VTE prophylaxis, chest physiotherapy. Switch IV→oral once clinically stable and afebrile. Typical duration 5 days for CAP (extend for Legionella/Staph/abscess).

High-yield: Pneumococcal (PCV13/PPSV23) and influenza vaccination are the key preventive measures, especially in elderly, splenectomised, sickle-cell and immunocompromised patients.

Aspiration Pneumonia — Site Localisation

Aspiration follows depressed consciousness, dysphagia (stroke, bulbar palsy), GORD, NG tubes, alcohol. The segment affected depends on patient position when aspirating (gravity-dependent segments):

Position when aspirating	Segment involved
Supine / recumbent	Posterior segment of upper lobe + superior (apical) segment of lower lobe
Upright / sitting	Basal segments of lower lobe
Either	Right lung > left (RB is wider, shorter, more vertical)

High-yield: The most common site of aspiration is the posterior segment of the right upper lobe and the superior segment of the right lower lobe because the right main bronchus is more vertical and aspirated material settles there in a supine patient.

Complications

• Parapneumonic effusion → empyema (frank pus in pleural space). Pleural fluid suggesting complicated effusion/empyema needing chest tube drainage: pH <7.2, glucose <40–60 mg/dL (<2.2 mmol/L), LDH >1000, or frank pus/organisms on Gram stain.
• Lung abscess — necrotising cavity with air-fluid level; commonest with anaerobes/aspiration, Klebsiella, Staph. Foul sputum, weeks of illness, clubbing. Treat with prolonged antibiotics (4–6 weeks); postural drainage; surgery if refractory.
• Sepsis, ARDS, respiratory failure, multiorgan dysfunction.
• Metastatic infection: meningitis, endocarditis, septic arthritis (pneumococcal).
• SIADH (esp. Legionella), haemolysis (Mycoplasma cold agglutinins).
• Non-resolving pneumonia → exclude post-obstructive pneumonia (bronchial carcinoma), TB, organising pneumonia, resistant/atypical organism, empyema.

High-yield: Pleural fluid pH < 7.2 in the setting of pneumonia mandates intercostal tube drainage — a classic single-best-answer.

Key Differentials

• Pulmonary tuberculosis — chronic cough, weight loss, haemoptysis, upper-lobe cavitation; sputum AFB/CBNAAT.
• Pulmonary embolism / infarction — pleuritic pain, haemoptysis, risk factors; CTPA.
• Pulmonary oedema / heart failure — bilateral basal crackles, raised JVP, S3, cardiomegaly.
• Lung carcinoma with post-obstructive collapse — non-resolving infiltrate, smoker.
• Organising pneumonia (COP) — migratory infiltrates, no response to antibiotics, responds to steroids.
• Eosinophilic pneumonia / hypersensitivity pneumonitis, pulmonary vasculitis.

Recently asked / exam angle

• Single most common cause of CAP → Streptococcus pneumoniae (recurring NEET/INI-CET stem).
• Urea cut-off in CURB-65 → >7 mmol/L; R cut-off → ≥30/min; BP → <90/≤60.
• "Red-currant jelly sputum + bulging fissure + alcoholic" → Klebsiella.
• "Hyponatraemia + diarrhoea + relative bradycardia + air-conditioning" → Legionella; diagnosed by urinary antigen, treated with fluoroquinolone/macrolide.
• "Young adult, dry cough, cold agglutinins, erythema multiforme, CXR worse than exam" → Mycoplasma; DOC macrolide/doxycycline.
• Most common site of aspiration → posterior segment RUL / superior segment RLL (supine).
• Pleural fluid pH <7.2 → insert chest tube (empyema).
• HIV + CD4 <200 + hypoxia + bilateral infiltrates → Pneumocystis; DOC co-trimoxazole + steroids if PaO₂ <70 mmHg.
• Post-influenza pneumonia with cavitation/pneumatocele → Staphylococcus aureus.
• Legionella culture medium → BCYE agar.

Rapid revision

1. Commonest CAP organism overall = pneumococcus; classic lobar pneumonia with rusty sputum.
2. CURB-65: Confusion, Urea >7, RR ≥30, BP <90/≤60, age ≥65; score 0–1 home, ≥3 hospital/ICU.
3. Klebsiella = red-currant jelly sputum + bulging fissure in alcoholics/diabetics.
4. Legionella = hyponatraemia + relative bradycardia + GI + confusion; urinary antigen positive; BCYE agar; treat with levofloxacin.
5. Mycoplasma = cold agglutinins (anti-I IgM), erythema multiforme, bullous myringitis; DOC macrolide/doxycycline.
6. Atypicals need macrolide/doxycycline/fluoroquinolone, not plain beta-lactams.
7. HAP/VAP = onset ≥48 h after admission/intubation; cover Pseudomonas + MRSA.
8. Aspiration in supine patient → posterior RUL + superior RLL; right lung favoured.
9. Pleural fluid pH <7.2 / pus / glucose <40 = empyema → chest tube drainage.
10. Lung abscess = air-fluid level cavity, anaerobes/aspiration; treat 4–6 weeks antibiotics.
11. PCP: HIV CD4 <200 → co-trimoxazole + steroids if hypoxic (PaO₂ <70).
12. Prevention = pneumococcal + influenza vaccines; consolidation signs = increased fremitus, bronchial breath, aegophony.